1. Field of the Invention
This invention generally relates to data processing systems in which storage components must be maintained in a predetermined sequence. More particularly this invention relates to a data processing system in which a disk storage device is divided into a plurality of storage logical volumes and in which the storage logical volumes are concatenated in a sequence to produce a single host logical volume distributed over a plurality of magnetic disk storage drives.
2. Description of Related Art
Data processing systems generally comprise one or more processors, input-output units and data storage facilities. Data storage facilities comprise various types of memory including magnetic disk storage devices or drives. Multiple drives are often grouped into arrays, commonly referred to as disk array storage devices (DASD), that store applications and data as data sets, files or blocks in logical volumes as known in the art.
Prior art data processing systems, such as Symmetrix disk storage systems available from the assignee of this invention, define one of two possible relationships between logical volumes and physical disk drives. In one, a single logical volume exists on a single physical disk drive. In a second, a single physical disk drive may store a plurality of logical volumes. This type of storage is sometimes referred to as "hypered" storage, and the logical volumes are often called "hypers". However, in either approach, the capacity of a logical volume is limited to the maximum capacity of a physical disk drive on which the logical volume (i.e., "hyper") resides.
There are now emerging a number of applications where the required capacity for the logical volume, or hyper, exceeds the capacity of a physical disk drive. United States Letters Patent No. 6,055,603 granted Apr. 25, 2000 defines one approach for providing such increased capacity. In accordance with that solution a number of storage logical volumes are concatenated into a predetermined sequence as a meta device wherein each storage logical volume is a meta member. The first storage logical volume or meta member in the meta device is called a "meta head"; the last storage logical volume or meta member, a "meta tail". A meta device acts as a single host logical volume that a host addresses through the meta head. With this approach a host logical volume size becomes independent of physical drive capacity.
Meta devices require the position of the storage logical volumes or meta members including the meta head and meta tail and their corresponding drives to be fixed in sequence within a group. If, during a maintenance or upgrade procedure physical disk drives are removed and then accidentally exchanged when they are replaced, application data can be lost if that exchange goes undetected. This occurs because there is no way for the host processor to recognize that an exchange has occurred with respect to any meta member other than the meta head. The resultant potential for a data loss requires some approach to provide a data integrity check that assures correct placement of all the meta members in a meta device.